Sliding behaviour and surface quality after static air polishing of conventional and modern bracket materials: In vitro analysis

OBJECTIVES: As part of orthodontic treatment, air polishing is routinely used for professional tooth cleaning. Thus, we investigated the effects of static powder polishing on sliding behaviour and surface quality of three different bracket materials (polymer, ceramic, metal), including a 3D-printed bracket. METHODS: Two bracket types of each material group were polished with an air-polishing device using sodium bicarbonate. Exposure times were set at 10, 20, and 60 s; the application distance was 5 mm. The force loss due to sliding resistance was tested with an orthodontic measurement and simulation system (OMSS) using a 0.016 inch × 0.022 inch stainless steel archwire. Untreated brackets served as control. Polishing effects and slot precision were evaluated using an optical digital and scanning electron microscope. RESULTS: Sliding behaviour and slot precision differed significantly between and within the groups. Prior to polishing, polymer brackets showed the least force loss, ceramic brackets the highest. With progressive polishing time, the resistance increased significantly with titanium brackets (26 to 37%) and decreased significantly with steel brackets (36 to 25%). Polymer brackets showed the smallest changes in force loss with respect to polishing duration. Slot precision showed the largest differences between material groups and was primarily manufacturer-dependent with hardly any changes due to the polishing time. CONCLUSION: Powder polishing can positively or negatively affect the sliding properties of the bracket–archwire complex but is more dependent on the bracket–archwire material combination (i.e., manufacture-dependent slot precision). For titanium brackets, resistance only increased after 60 s of polishing. For ceramic brackets, effective reduction was observed after 10 s of polishing. Polymer brackets, including the 3D-printed brackets, showed better sliding properties than ceramic or metal brackets even after polishing for 60 s. Removal of plaque and dental calculus should lead to a noticeable improvement of the sliding properties and outweighs structural defects that may develop.